<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>3.margin负值问题</title>
  <style type="text/css">
    body {
      margin: 20px
    }

    .float-left {
      float: left;
    }

    .clearfix::after {
      content: '';
      display: table;
      clear: both;
    }

    .container {
      border: 1px solid #ccc;
      padding: 10px;
    }

    .container .item {
      width: 100px;
      height: 100px;
    }

    .container .border-blue {
      border: 1px solid blue;
    }
    .container .border-red {
      border: 1px solid red;
    }
  </style>
</head>

<body>
  <!-- 3.margin负值问题 -->
  1.margin-top和margin-left 负值，元素向上、向左移动
  2.margin-right负值，右侧元素左移，自身不受影响
  3.margin-bottom 负值，下方元素上移，自身不受影响

  <p>用于测试margin-top bottom负值情况</p>
  <div class="container">
    <div class="item border-blue">
      this is item 1
    </div>
    <div class="item border-red">
      this is item 2
    </div>
  </div>

  <p>用于测试margin-left right负值情况</p>
  <div class="container clearfix">
    <div class="item border-blue float-left">
      this is item 3
    </div>
    <div class="item border-red float-left">
      this is item 4
    </div>
  </div>

</body>

</html>